And its orbital period is probably about 20,000 years.

I’ll let the guys at Caltech fill you in on the details in this video (1m 09s), but scroll down if you just want a quick summary.

[Summary: the very furthest objects in our solar system we have observed were all aligning up in a very specific way that could be explained by the presence of a planet shepherding them into place. Thanks to computer modelling and mathematical calculations, its size is estimated to be somewhere between that of Earth and Neptune and it is likely to be an icy planet, but it’s a long, long way out there.]

Why has it taken us so long to find?

There is a lovely long history of scientific debate regarding undiscovered planets beyond the orbit of Neptune, often referred to as “Planet X”. It was found that the masses in our solar system just didn’t add up to the gravitational effects that were being observed and so surmised that there was something big enough to offset the difference lurking somewhere. Pluto was supposed to be one such balancing object although it has been revealed to be far too small and has since been demoted down to dwarf-not-really-a-planet status (I still heart you, Pluto).

Then along come Mike Brown – ironically the guy who authored How I Killed Pluto and Why It Had It Coming – and Konstantin Batygin to propose a very neat solution to why certain Kuiper Belt objects were lining up the way they were: a massive planet, at least as big as Earth if not bigger, but really, really far away from the sun, and therefore hard to observe. It seems to explain what was previously just guessed at.

But this theory is not a slam-dunk. There are some problems, according to Ethan Siegel of Forbes. The nice, neat, large planet solution to the gravitational quandary of our solar system is just one of many possible options. This theorised new planet could turn out to be a bunch of smaller objects moving in the same general direction, or another mechanism entirely. There are also reasonable expectations that we would have detected a massive body using techniques such as infrared. But hope still exists.

One thing is for sure though – if there is a planet out there, it would not be home to any little green men.

What, no aliens?

Proponents of the “Nibiru” theories will be getting ready to say, “I told you so,” about now. If you’ve not heard about this, there is a group of very ardent supporters of the theory that ancient Sumerians knew there was an extra planet, which they called Nibiru. Unfortunately, the theory they propose has so many problems with its scientific and historical inaccuracies it can pretty much be dismissed even before you get to the alien interference with the evolution of man. Anyway, have fun googling that.

The likelihood of a planet like this one with a bunch of alien life on it would be ridiculous. We know how hard it is to get life to hang on to planets that stick in a close and regular orbit around the sun. This “new” planet’s distance from the sun varies from 15 times the distance from the sun to pluto to 75 times. That’s one cold, dark, icy abode. Would make the ice planet Hoth from Star Wars look balmy by comparison.

What is astounding about this news (if it is proven) is that we’ve been discovering planets around other suns before we’ve discovered one around our own. But with an orbital period of 20,000 years, and a distance from the sun of between 15 and 75 times the distance to Pluto, we were unlikely to have just looked up and counted it into our heavenly pantheon.

Find a planet in your own back yard

What’s so exciting about all this is the part that you could play. Although there may or may not really be a massive planet out there,there’s the potential that an amateur astronomer with a backyard telescope could be the first to observe this mysterious heavenly body.

So I encourage you to look up and get excited about the universe. The potential is still there even in our own neighbourhood for the thrill of discovery.

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